1. Field of the Invention
The invention relates to a device and a process for producing optical molded parts, in particular completely transparent optical molded parts, from plastic.
Optical molded parts, in particular completely transparent optical molded parts such as glazings, for example, have been produced from glass as a rule, for a long time. Because of lesser weight, higher impact strength and increased design freedom, optical plastic molded parts have acquired increasing importance in recent past.
In order to produce optical plastic molded parts, use has been made so far of injection molding and embossing processes known in plastic processing. However, the known processes have substantial disadvantages in the case, in particular, of large-area optical molded parts such as glazings for motor vehicles, for example. Because of the inherently short runners in the injection molding process, it is necessary to expend a high injection pressure in producing large-area molded parts. However, this leads to high stresses and thus to warpage in the molded part. Moreover, strong sinking occurs in the subregion of the molded part remote from the gate. The molded parts frequently have faults in the surface that are to be ascribed to frontal flow when use is made of the known embossing process.
However, because of their relevance to safety, high optical demands are made, for example, of glazings of motor vehicles, so that neither the conventional injection molding process nor the conventional embossing process seems suitable for producing such optical plastic molded parts.
A device for carrying out a tilting embossing process is described in document German Patent DE 195 17 024 C2. The tilting embossing process prevents the production of strong stresses in the molded part and improves the surface quality. The device has a relatively complicated tilting mechanism. An axis of rotation of a swivel-mounted mold plate is pressed by a clamping device into a bearing bush that is constructed in a fixed mold plate.